Here's a topic guaranteed to start controversy. Which Linux distribution is best? It all depends on your criteria for judging. Even then the topic is highly subjective. Here are a few nominees for "best distro" in specific categories.

I develop HPC (high performance computing) applications (C, C++ and Fortran). To do realistic benchmarks I need total control of what is going on in the system: disk access, network packets, memory allocation, swap usage, core affinity, etc.

I know what I'm doing and what I'm installing, I don't want sudo or automatic package dependencies. To avoid problems I require vanilla versions of all libraries, many times I will need to compile them by myself, or install several versions at the same time for compatibility.